How do we know that's what the climate would have been with zero human influence?

Question

https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9s9-4-1-2.html


The blue line came from model outputs. What assumptions went into those models?

I'm going to guess an answer here that CO2 was simply held constant and then the output is assumed to be the natural forcings. But isn't that a circular argument?

Answer 1

We don't know what the climate would have been like without any anthropogenic effects.



As for circular arguments I think many will be discovered at some point. I still remember Trenberth finding the missing heat in the oceans. First, he had a good look but couldn't find any. Then he used a model to help with the interpolations and he found some.



So let's think about that. If you have a model that says the missing heat is in the ocean but you can't find it, then if you use the model as part of the analysis it finds the heat which confirms the model. That has a definite circular reasoning component to it. JimZ is right about scientists. It is not a qualification it is an attitude of mind.



Incidentally. I wonder how that paper stacks up now that we know there has been no pause? The other point about the reanalysis is what did the previous temperature increases look like. We had all the dire warnings at the time but has anyone gone back and seen how many of those warnings were erroneous now that the data has been reanalyzed. Are all those previously declared hottest years still the hottest years, for instance? Do the models account for the fact that the temperature difference between the surface measurements and the satellite measurements is no longer constant but changing?

Answer 2

We don't, for certain.



But we can make some pretty solid guesses.



I'm ballparking from an educated layman's perspective (I've taken... basically one class that could reasonably be considered significantly about climate, biogeochemistry), but I'd say we probably know to within at least 70% what the influence of all the major factors is. That is, our estimates of how much CO2, sulfates, etc affect climate are no more than about 30% off from the true value. Large margin of error for making precise estimates, but pretty reasonable for getting ballpark figures.



There is no substantive reason to think atmospheric CO2 would have changed significantly without human influence (or the influence of some equivalent technological intelligence). We can also get fairly precise figures for things like natural vs anthropogenic aerosols. And so forth. So, if we subtract (or add, as appropriate) the probable influence of human-created or human-altered factors, we can get a reasonable guess of what the climate would have been without humans influencing things.

Answer 3

I hear some alarmists claim that it should be cooling and I suspect their models would show precisely that if you removed CO2 from them. Since we really don't know what the climate would be without human influence, it is all speculative and I think wildly so.



Even though I know temperature is governed by them, I don't even like talking about things such as forcings and feedbacks because it is a language that is too often used to portray authority, an authority gained by knowledge, and that knowledge isn't entirely deserved. It is a language that is too often used by those who suggest we know more about what causes the planet to behave in the way it does so that they can use it for an agenda that doesn't include science. Their agenda is all about CO2 causing catastrophic warming. If they were to dare admit that it might not be that catastrophic, the money behind their "science" would dry up.



From Pegminer,

"So can we also say that if you admit that it might be catastrophic then the money for your "science" will also dry up?"

I must admit that question stumped me for a bit because there really isn't any "money" funding my "science". I know alarmists like to portray big oil and Kochs as the alternate to their funded science but that is more about pixy dust and fairies. My science doesn't rely on money. It is simply the search for truth. It is simply science. When money gets involved in science, science diverges from a search for the truth to satisfying money's desires.



Young is a great example of a confused individual. He thinks he understands science but let be the first to say how unimpressed I am with his "science" knowledge. What stupidity it is to think skepticism of unproved theories is the Dunning-Kruger effect.



Gary and Young suggest it is hindcast but the models that predict catastrophic or significant warming don't work in retrospect. There is so much dishonesty by alarmists and I don't even mean Young and Gary. The exaggeration is systemic and ubiquitous.

Answer 4

From your link :



" ... The interannual variability in the individual simulations that is evident in Figure 9.5 suggests that current models generally simulate large-scale natural internal variability quite well, and also capture the cooling associated with volcanic eruptions on shorter time scales. Section 9.4.1.3 assesses the variability of near surface temperature observations and simulations. ... "



Looks as if they are saying the "volcano cooling" is being over-ridden by the CO2 forcing. Whether or not anyone agrees or disagrees doesn't matter. That's what they seem to be saying.

Answer 5

The variables used in the multiple simulations that were used for that graph about 9 years ago included:



Greenhouse gases

Direct effect of tropospheric sulfates

Indirect effect of tropospheric sulfates

Volcanic stratospheric aerosols

Solar irradiance

Black carbon

Tropospheric ozone

Stratospheric ozone

Land use (surface albedo, surface roughness, stomatal resistance, and effective water capacity)

Answer 6

Ah hah. So deniers now admit there is warming! Chopping and changing when they feel like it.



Can't win with deniers. It's an unwritten rule.

Answer 7

We cannot know that exactly - and no one has ever claimed that we can or shown that is it necessary when investigating general trends that do not have that level of detailed resolution in their frequency distributions (this is not specific to temperature or climate science - it applies to all signal processing and frequency-time domain studies in all scientific fields).



Young is correct. Model forecasts (if this is what you are implying) have never been used as evidence in identifying normal from anthropogenic warming. As i have repeatedly pointed out, model forecasts of temperature are not valid scientific evidence because they do not exist in the real world.



The evidence for the CO2 effect comes form models that exclusively use existing observational data. This is accomplished by building models based on the full set of data. Models are then built using subsets of the full record and these are used to estimate the values that were not included in that subset. Various model validation test procedures are the run to evaluate model fit.



When the known natural forcing variables that drive temperature are used, the models fail to adequately account for (i.e., explain) the observed variance. Introducing atmospheric CO2 data as a variable better reconstructs the behavior of the observational data. This is not whimsical, since we have a priori knowledge from physics and chemistry that CO2 is a significant variable.



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Jim z –



>>Gary and Young suggest it is hindcast but the models that predict catastrophic or significant warming don't work in retrospect. <<



The question concerns how to partition total warming into natural and anthropogenic components; therefore, model predictions are not relevant.



Which models “that predict catastrophic or significant warming don't work in retrospect – and what is the definition of catastrophic?



Although there are exceptions, most models do work in “retrospect.” They work not only for global temperature, they have successfully predicted regional differences such as increased arctic and night warming, stratospheric cooling, and even environmental effects from warming such as those observed in some biotic communities.



http://www.sciencedaily.com/releases/2013/08/130822105042.htm



http://www2.ucar.edu/atmosnews/just-published/12313/progress-decadal-climate-prediction



http://news.berkeley.edu/2012/06/12/hindcasting-helps-scientists-improve-forecasts-for-life-on-earth/



http://ceoas.oregonstate.edu/people/files/jones/gutierrez-illan_et_al_gcb_14.pdf



Also, models just as frequently underestimate observations, as is the case with the decrease in arctic ice.



http://www.copenhagendiagnosis.com/